They won't stay though, because their opinion is unlikely to be the same as your opinion, and people only spend money on things that they think are good.
You might believe your app is the greatest thing in the world, but that doesn't matter at all. You're not trying to persuade yourself to buy; you need to persuade your customer that the app is good. Clue: They're not looking at the code.
Also, 'good' is a measure of usefulness rather than quality. People will spend a lot of money on absolute trash if it solves a problem that's costing them more money or time than your app, no matter how bad your app is.